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Could a F-22's exhaust stall a highjacked Boeing 767's turbofan(s) and force it to land?
Would it be possible to use a F-22's exhaust to intentionally stall a hijacked Boeing 767's turbofan engines in order to force it to land instead of shooting it down?
The idea being that stalling one or both obviously causes thrust from a remaining engine to force pilots to compensate thereby limiting maneuverability or even allowing intentional redirection of the aircraft by the F-22s exhaust using disruption of airflow over control surfaces.
Kind of an out there question but there could be a scenario where this is a better option than eliminating the threat.

There's a few real problems with this approach.  As has been pointed out, "flaming out" a passenger jet's engine with another jet would be extremely unlikely to work.  But as importantly, both of your theories--disrupting the engine or disrupting airflow--would require very precise coordination by the hijacking crew.   Say you could get the F22 perfectly lined up with the 767's wing or engine, and it was actually going to work...  The hijacker is simply going to keep moving the stick. Imagine if I tried to follow you driving in front of you.  You'd just turn.

No. Jet engines do not stall easily. It's difficult even for a fire crew to shut down an engine. Turbines burn very lean, so jet exhaust has plenty of oxygen in it. It will not stall an engine.
Afterburner exhaust might be an issue due to the heat and might affect engine operation, if the fighter gets very close. Dumping fuel could also be destructive. Either way, disrupting a plane that's flying so close is unreasonably dangerous to both aircraft.
Even if briefly stalled, the engine can be restarted. There's no reliable way to physically force a landing without risking destruction of the target.
That said, it's not necessary. Fighter escort is a well-known way to land uncooperative aircraft.
Threats don't work well on the ground, because the perp can slip away, or can be impaired by emotions or substances. Thus, less-lethal weapons. But there's no hiding in the air. And if you can land a jet, you can comprehend "Land or be shot down".
These threats are not idle. Passenger jets have been shot down, by accident or intent, even before 9/11. Fighter pilots do usually ask for a second confirmation of the shootdown order, but once confirmed, they carry it out. Ethical deliberations aren't their job.
So offending airplanes are forced to land through a threat of deadly force, which works just as well.

Might be worth mentioning that even if the engine flames out through exhaust ingestion starting it up again would be straightforward and might even be automatic depending on engine. Dumping your fuel into the 767 intake might do something, but 'something' ranges from nothing to both aircraft vanishing in a fireball so using weapons if available seems wiser

It's an exaggeration to say that passenger jet shootdowns happen "every few years", especially recently.  The last incident in that wiki article similar to what this question is about is 2001, and that was a Cessna floatplane with 4 people aboard, shot down by a Peruvian air force Cessna in a miscommunication with the CIA over suspected drug running.  All the later incidents were ground-launched SAMs, and the summaries sound like accidental target mis-identification or rogue actors, not like govt. warning the target and then intentional shootdown while being aware of the target's ID.

https://en.wikipedia.org/wiki/Korean_Air_Lines_Flight_007 from 1983 might be the last time a passenger jet was intercepted by fighters and then shot down after they weren't happy with its response.  (They apparently fired warning shots at the suspected spy plane, but the theory is the KAL pilots probably didn't see them.)  I didn't carefully check all the others in the list, but their summary descriptions didn't sound like intercept, warn, destroy.  Often like shootdown soon after takeoff in a war zone, or terrorists or rebels or whatever. Or one case in Pakistan of a SAM launch on a lost jet.

@PeterCordes 1983 was the last shootdown by a fighter. But there were two shootdowns by surface-to-air weapons in 2020. The reality of war is - any military, from Somali to USA, will shoot unless they're sure it's a civilian target, not only if they're sure it's a military one. My point is, a warning from a fighter jet is a real threat, they will fire unless you comply. They put you in a "land or die" situation already.

Your answer says "these threats are not idle", talking about a shootdown of a plane IDed by fighters as civilian markings, but uncooperative.  I think that's true, post 9/11 a hijacked plane will be shot down rather than allowed to be used as a kamikaze weapon.  And yes, the shootdowns prove that they have the capability to do it.  But your phrasing sounded like you were saying this situation (threat and then follow-through) actually happens every few years.  Your edit to add "by accident or intent" is a good addition, thanks.  I got your meaning originally, just a wording nitpick. :)

@PeterCordes Yes. My point is that anyone smart enough to fly a jet, is smart enough to understand they will be killed unless they comply. Combat pilots are selected, among other things, for their ability to carry out orders. Passenger planes got shot down even pre-9/11 - it's even more certain now.

So why is there nothing between hoping the hijackers comply and land, and destroying the aircraft with a missile? Couldn't there be a step of escalation in-between? For example, using the cannon to shoot the engine. This would still have a chance of destroying the airliner, but not as high of a chance as shooting a missile at it. But at least it would be safe for the fighter (unlike the proposals of the OP)

@vsz I guess a cannon is less lethal, but it's still likely to cut hydraulics lines and start a fire. We're talking 90% vs 99% chance to kill everyone on board. It's probably safer to wait till the plane runs out of fuel on its own, or hope the hijackers are overpowered.

Most likely, the answer is no
As pointed out above, jet engines burn quite lean, so there are still is plenty of oxygen in the exhaust gases available for combustion. So much so that during the 1950s – I remember Chuck Yeager talking about this in his autobiography – the Air Force would sometimes start jet fighters by parking another aircraft in front of the one to be started and using the exhaust gases to spin up the starting engine. In modern times with the use of pneumatic huffers (start carts) and APUs, this is not common practice anymore.
Then there is the risk to the jet fighter in attempting to maneuver that close to an airliner, in order to wash out his engines with the fighter’s jet exhaust.  This would be a very difficult position to maneuver an airplane into without a high risk of a mid air collision.
There is also the problem that, even if you could cause a flame out in the airliner that way, the engines can be easily restarted by a competent flight crew.
Even if a restart was not possible, once the engines are knocked out, the aircraft is either going to have a forced landing somewhere or crash creating a high risk of serious injury or death for everybody on board.  Given this and problems I stated above with a mid air collision risk, it would be much easier for fighter air crew to employ conventional deadly force ie guns or missiles, if it was required to stop this airliner.


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Why wasn't the F-14 upgraded for an electronic warfare role after the Cold War?
The new DLC for VTOL VR got me thinking: why wasn't the F-14 Tomcat retrofitted for the electronic warfare (EW) role? The concept of electronic attack and defense was starting to rise to prominence around the time of the Soviet Union's collapse, which was the reason the Tomcat was retired in the first place. The EF-111A Raven and the EA-18G Growler are proof positive that aircraft original designed as fighters and attackers can work in an EW role. So, why wasn't this applied to the F-14 to create an electronic warfare variant, a sort of "Jamcat" if you will?

Remember EA-6 had 4 seats. If F14 could fit the bill, so could a 2-seat EA-6.

Cost, weight, age, and commonality.
Cost and weight: The F/A-18 was designed to be a relatively affordable and maintainable multirole fighter, in part addressing the deficiencies of the F-14 in this area. The Super Hornet has put on a lot of weight, but it went to the right places; as a result, its useful load is greater than that of the Tomcat - 34,000 lbs for the SH vs 30,000 for the Tomcat.
The Tomcat's load is limited not so much by its wings and engines, as it is by the carrier's catapults; it comes too close to their 80,000 lbs absolute limit, and needs more than the minimum launch speed. It also took more maintenance, so, even with the new engines, the Tomcat had a lower availability than the Hornet. The lesson has been learned.
Age: For an EW aircraft, you want good baseline avionics, which are then augmented with underwing pods for jamming and other purposes. The F-14A's avionics are seriously out of date. Even the F-14D, while it got some MFDs fitted, is based on an older design, with the lack of fly-by-wire limiting its autopilot performance. As a minimum, the APG-71 radar would have to be replaced with an AESA. Even using existing modules, a new radar variant still involves integration and testing expenses.
Commonality: None of that would've been a deal-breaker if the Navy intended to fly the Tomcat as its primary fighter. As it happens, once the Cold War ended, its unique long-range CAP role was no longer necessary. The Navy retired them as fast as it could get enough Hornets, and sometimes even faster.
You don't want to have to keep expertise, spares, and supply chains for more aircraft families than necessary, which is part of why the EA-6B was replaced in the first place. The Intruder is a much easier bird to maintain than the Tomcat, so the Navy was happy to keep the Prowler for a while even after retiring the A-6. With the Super Hornet forming the bulk of present and near-future USN air wings, it was the obvious choice of platform for a replacement.

Interesting comment about the catapult being a weight limiter.  Do the newer carriers have stronger catapults?

@RobertDiGiovanni The EMALS on the Ford class has more power, ~120 MJ vs ~100 MJ. The aircraft weight limit is still 80,000 lbs, but the catapult has been tested with 100,000, so it can work better at the limit. However, it's very new, and still has reliability issues. So it wasn't ready at the time, and even now it will take a long time to get multiple Fords operational.

Just to build on the answer by Therac; at the end of the Cold War the US Navy also had the ES-3 based on the S-3 Viking, the EA-3 based on the A-3 Skywarrior as well as the EA-6 based on the A-6 Intruder. All of these were established platforms, so if additional capacity were needed, chances are that they would expand on the already proven platforms rather than adding a new unproven (and dated) aircraft. Two of the three (ES-3/EA-3) could also function as refueling aircraft, adding to their value within the fleet.

the EA-6 could also be used for refueling, and was at times. It could also be employed in a SAM hunter role later in life, loaded with up to 4 HARM missiles (at the cost of some of its EW capabilities, obviously). F-14 also had a refueling capability but could not carry HARM.

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What prevents the F-16 JFS from running indefinitely?
The JFS (Jet Fuel Starter) on the F-16 is basically an APU that runs on jet fuel, but started by compressed air, from what I understand.
As an aside: Please correct this too, preferably with some reference. Is it correct that it is started on compressed air? And that it gets refilled, compressed again, when the engine runs above a certain RPM?
Main question:
Why doesn't the F-16 JFS keep running? If it runs on jet fuel, couldn't it keep running as long as the F-16 has fuel? I believe the JFS is shut down automatically once the engine is running, but if it weren't for this feature, it would just keep running. Is that correct?
Edit addressing some comments:
Why am I asking this? Why would I want to have the JFS running?
It is simply a question to help me understand how the JFS works. It is unclear to me why it has an inlet and exhaust port. This indicates to me it runs like a normal APU. Yet, I find various information indicating it runs on compressed air, some sources say it runs on hydraulic fluid. If it runs on compressed air or hydraulic fluid, why would it need both an inlet and an exhaust port?
It isn't that I would like to keep the JFS running on the low-mileage F-16 I have in my garage, rather that I don't understand the mechanics of the JFS and how it differs from a regular APU.

Why would one want the JFS to keep running? Like the starter in your car...it disengages and shuts down once the engine is spinning fast enough to maintain itself.

Since now-deleted answer https://aviation.stackexchange.com/a/101089/34686 won't be visible all, I'll repost the link included in it: https://theaviationgeekclub.com/heres-why-starting-the-engine-on-an-f-16-viper-is-different-from-most-other-jet-aircraft/ .  Worth reading in full.  Says JFS is shut down when main turbine reaches 40% but doesn't say whether shut-down is automatic or manual.  Does indeed say JFS is started by compressed air (but runs on jet fuel.)  Maybe poster will resurrect that answer after some editing?

But it's not exactly clear what the real core of your question is.  Are you asking the exact shut-down mechanism for the JFS?  Or are you asking the purpose of shutting it down?  (Or both?)  An answer addressing the latter has been dv'd but as far as I can see it was a valid answer to the question.

Continuing to run the JFS after main engine start would consume fuel, unnecessarily reducing the plane's range for no appreciable benefit.

@WPNSGuy Thank you. I've addressed your comment in the question itself. I should have made it more clear why I'm asking this. As I've explained in the question now, I simply don't understand how the JFS works, and this question might help me understand.

The flight manual is available online currently at,
https://info.publicintelligence.net/HAF-F16.pdf
It states in Section 1-36 (pg 65 in the linked PDF),

The JFS is a gas turbine which operates on aircraft
fuel and drives the engine through the ADG. The
JFS is connected by a clutch to the ADG and only
provides torque when required to maintain engine
rpm. If the ADG is not able to rotate (i.e., seized
engine), the JFS runs, but the clutch prevents it from
rotating the ADG. The JFS receives fuel at all times
regardless of the FUEL MASTER switch position.
The JFS is started by power from two brake/ JFS
accumulators used either singly or together. The
brake/JFS accumulators are charged automatically
by hydraulic system B or manually by a hydraulic
hand pump located in the left wheel well.

Also in the following paragraph it is stated,

The switch
returns to OFF automatically during a normal
ground start at 50 percent rpm.

So it would appear the JFS is ground started by pneumatic pressure which drives hydraulic fluid through a hydraulic motor.  That during a ground start, the JFS is automatically turned off.
For in-flight operations the manual states,

Once running, the JFS does not shut down until the
JFS switch is manually positioned to OFF.

This is most likely because for an in-flight restart the JFS does not develop enough torque until below FL200, and it simplifies the instrumentation and procedures required.

Welcome to SE.Aviation, great first post!

Despite its name, the F-16 JFS doesn't consume jet fuel. It spins due to compressed air. There are two bottles of air at 3,000 PSI that are used to spin it, and it in turns spins the main engine until it gets to 20% RPM, at which point the throttle is set to idle and the engine starts. Normally you use one bottle, but if you select bottle 2 then both bottles are used. If the start fails then the ground crew has to pump it back up with a breaker bar, which I hear is not a fun job. It's only job is to spin the engine until it can start on its own. It does not have an electric generator like the vast majority of APU's, with the exception of those identified as "huffers" because all they do is blow air into the engine or air starter to get it going.
Think of it as the starter on your car, except it does not disengage when the engine starts.
A true APU can provide electrical power, as well as whatever starting means the engine needs -- air, hydraulic or electrical. For example, the APU on a CH-46 medium transport helicopter (now retired from USMC service) starts with hydraulic pressure (as opposed to air pressure on the F-16) from a reservoir charged by a hand pump to 3,000 PSI, and after it starts it provides electrical and hydraulic power for the rest of the systems on the helo. It can run until the fuel tanks are empty. Once the main engines start the hydraulic reservoir is recharged back to 3,000 PSI for the next start.
So the answer to the question is that the JFS is always turning when the main engine is turning.

Thanks for your answer. I've edited my question to reflect why I'm asking this now (short version: I don't understand how the JFS works). Some sources say it uses compressed air, others, that it uses hydraulic fluid, others, that it runs on jet fuel, in all cases, to spin a compressor of some kind. Why does it need an inlet and exhaust port if it uses compressed air? Isn't the JFS directly connected to the gearbox of the engine? In that case, the main engine, obviously has a main inlet and exhaust? I don't understand why the JFS needs its own inlet and exhaust if it runs on compressed air.

Are you sure the JFS doesn't run on jet fuel? Are you sure it doesn't start using compressed air, and then, runs on jet fuel? https://theaviationgeekclub.com/heres-why-starting-the-engine-on-an-f-16-viper-is-different-from-most-other-jet-aircraft/ "‘The JFS is a small jet turbine started by an onboard compressed air bottle. Unlike an APU though, the JFS is directly linked to the main engine, so independent operation is not possible."

@AlphaCentauri I agree, the JFS runs on jet fuel but is started by compressed air just as similar micro jet turbines employed for starting the jet engine

Actually, you’re both wrong. The JFS is a small gas turbine which runs on the aircraft fuel supply once started. However, it is started up hydraulically with pressure provided from a accumulator charged with nitrogen gas.

Incorrect. Look at the aircraft pilot's handbook and video. When the air bottles are discharged the indicators that are monitored are the MAIN engine RPM and the Fan Inlet Turbine Temperature. The JFS is NOT a traditional turbine. And nitrogen gas does NOT qualify as a hydraulic start medium.

The Jet Fuel Starter (JFS) is designed to automatically shut off once the main engine has reached 50% of maximum RPM.  Theoretically, once started up, and the shut down sequence, not triggered, the JFS will run and run until the a/c runs out of fuel.
Just a note: for all practical purposes, the JFS functions like a APU; it’s a small gas turbine engine which provides power to start the main jet engine with.
The start up sequence for the JFS is a pair of hydraulic accumulators controlled by a cockpit switch (only one accumulator is typically required to start the JFS).  These accumulators maintain pressure via a nitrogen gas charge in side them.  Once discharged during engine startup, they are recharged by the aircraft hydraulic system when the engine accessory gearbox and hyd pumps are operating.  They can also be charged by an external hand pump in the event there is no charge left in the accumulators and the engine is not running (Apparently this manual charging is very laborious and a great way to piss off your crew chief!).

According to this source

Unlike an APU though, the JFS is directly linked to the main engine, so independent operation is not possible.

However, the JFS is a jet engine by itself, only this engine is pneumatically started. Therefore the chain is:

The JFS is started by compressed air
The main engine is started by the JFS
Once the main engine is sucessfully started the JFS is powered down

This powering down means that the JFS is not supplied with jet fuel anymore, as it would offer no advantage to do so. The main engine is more efficent anyways, and the JFS is too small to add any additional power output. Additionally, the wear and tear of the JFS is reduced this way.
As a last remark: I could not find a source stating if the JFS also stops spinning. I can imagine two scenarios:

Either the VFS is rigidly connected and simply spins with the main engine
Or the VFS is coupled for example by some sort of free wheel, meaning it would stop to spin when powered off

Unfortunately, I cannot provide an answer which of the two is true, however I think option 2 is much more likely, as it would reduce wear and tear of the JFS and also reduced friction. Also, the JFS starts the main engine to about 40%, therefore the JFS would spin pretty fast if it would not be decoupled, which would impact the max speed requirements of the JFS therefore making it more heavy/expensive.
Another interesting link is from a similar JFS of the Mirage fighter jet.

Re "This would mean that the JFS is not shut down after the start of the main turbine, but rather continues running."  -- no, actually from further down in the source you linked: "At around 40%, the JFS is shut down, as the engine can now spool up on its own."  The source doesn't say whether the shut-down is automatic or done manually.  The source may be using "directly linked" in a somewhat ambiguous way-- think of the starter in your car.  In a sense it's "directly linked" but in a sense it's not.  Can't run starter w/o it engaging the engine, but starter doesn't run whole time engine runs.

Also-- the link you quoted says the JFS is started by compressed air.  Not that it is powered by compressed air.  Two different things.

@quietflyer you are right, I thought the jfs was merely a turbine as in, expanding compressed air, but it is indeed a micro jet turbine. It is therefore started but not sustained pneumatically. But the "continue running" was meant as "it moves with the turbine". I edited to clarify.

@quietflyer Thanks for you comments, I reworked my answer quite a bit to include your statements and also to make it more "right"

@quietflyer is incorrect. The giveaway that the JFS is not an independent traditional turbine engine is that there are no instruments in the F-16 to monitor anything about its operation.

@JuanJimenez I think you are incorrect: "The JFS is a small jet turbine started by an onboard compressed air bottle. Unlike an APU though, the JFS is directly linked to the main engine, so independent operation is not possible." https://www.google.com/amp/s/theaviationgeekclub.com/heres-why-starting-the-engine-on-an-f-16-viper-is-different-from-most-other-jet-aircraft/

@JuanJimenez Also there is an instrument for monitoring the JFS RPM: It is the main RPM meter for the main engine as the JFS and the main engine are coupled

@U_flow that makes no sense, because that would mean there is no other means of monitoring the safety parameters of a separate turbine engine, regardless of what is is coupled to.

@JuanJimenez Well, I cannot tell you what the design decision rational behind this particular question is. However from all I see of online available documentation and also the other people participating in this question (e.g. Carlo Felicione), the JFS is definitly a small jet turbine. As a last thought: The energy density of pneumatical storages are pretty low, therefore the gas bottle in the F-16 is enough to start the small JFS jet turbine but not the large main jet turbine...

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What caused the Belgian aircraft mechanic who stole an F-16 to crash?
This is the story, from the late 80s:
https://apnews.com/3b2ba1c5735b3817a3e7ae3562780e9b
Why did he crash? Why would anyone crash in this scenario?
I'd like to ideally hear from someone who is either an F-16 pilot or has been lucky enough to be able to try flying the F-16. Even if this has been ruled a suicide I'm still curious what beyond landing are the main challenges with flying the F-16 for someone untrained.
As someone who will never get that chance myself but likes flight simulators, I'm curious exactly where the big difference from the simulation to reality lies. I'm quite certain many others who fly flight simulators are also curious what the difference actually is. What stops someone that knows what all of the functions of the controls are, and is intimately familiar with the startup procedure for the engine of the F-16 (like a mechanic), from actually flying an F-16? Yes, landing, but what else? Do you need to remember to change some engine settings, fuel settings, after taking off, otherwise the engine stalls? Can you easily exceed EGT, or otherwise damage the engine, if you don't know what you're doing? Do you need to change some settings for the battery, internal power? I'm just guessing blindly here.
Forgive me for the hand waving like arguments I'm using, but, how hard can it be to keep an F-16 in level flight, if you are able to climb to 2,000 feet in the first place?
For the particular cited story above, it seems strange that the mechanic was able to take off and climb to 2,000 feet, and only then crashed. Does this point strongly to suicide?

It's one thing to taxi an aircraft around and know what the controls theoretically do, its another thing entirely to get it into the air and control it. For example he knows how the engine works, but does he know what happens when you exceed a critical AoA? Go to slow and stall, does he know the recovery procedure? Pushing throttles forward and pulling back on the stick means take-off, after that its an entirely different game. It takes no time (or effort) for an F-16 to climb to 2000 feet. He was only airborne for 2 minutes, 5 seconds.

F16 is 3 decades before airplanes are as easy to fly as video games.

@RonBeyer Seems to me that 2 minutes 5 seconds is an EON when compared to how fast things happen in a fighter....

Learning how to fly an aircraft isn't a trivial undertaking.  You may be surprised to learn that simulation back in 1982 was nowhere near as good as it is now.  taking off? Not that hard to do if you know how to use the rudder to stay pointed down the runway.  Learning how to land?  A bit trickier.  We would not let them solo until the 14th flight when I was an instructor, and that's if they did well.  Screw up a landing and it's easy to be dead.  Learning how to fly ? For a FBW in 1982? Go and get some training on how it works.  That crash was "you can't fix stupid" playing out in real life.

Even though it will probably pass, I disagree with the close vote. While we may not know the answer at this point, the question itself is specific and answerable. That the investigation is over and no one is known to be looking for the answer right now isn't reason enough to permanently shut the door on the question.

You should add a brief description of the flight as links may be dead in the future.

the last sentence is subjective. you may change it as "is it a clue supporting suicide?"

Unauthorized flights of military jets by mechanics have happened in the past.  Some of the aircraft landed successfully after the ordeal others resulted in fatal accidents.  The two successful cases which I’m aware of, the mechanics had previous flight training.  We still cannot determine whether this F-16 went down as a result of inability of the pilot to control the aircraft or whether it was an intentional suicide by airplane.
There is nothing outrageous or unusual about an F-16, save that it is a high performance fighter, with a high thrust to weight ratio, (relatively) high wing loading and low aspect ratio wings and handles accordingly.  The sidestick controller combined with the fly by wire flight controls and nimble handling requires a light touch on the controls - some pilots describe it as almost a ‘kissing’ sensation - to properly fly, which possibly could get away from a neophyte.  Like most high performance airplanes, it needs to be flown by the numbers and can be demanding to land, though not as difficult as some other military jets eg T-38, etc.
The physical act of flying seminal maneuvers is very easy in these jets with a little flying knowledge.  Most fighter pilots describe their jets as easier to fly than say a Cessna.  Flight control laws eliminate a lot of the babysitting and grunt work one has to do in an aircraft with conventional controls.  The pilot has an unobstructed view from the canopy of the environments, offering very good situational awareness.  All primary flight data is displayed prominently in the HUD and easy to decipher.  More complex flying will start to become demanding and potentially lead to trouble.
Aviation has a lot of scenarios which seem benign but turn into death traps if you don’t fully understand what’s happening.  There are plenty of sad tales such as stall spin accidents, low level aerobatics, etc. where people thought they could handle a situation but their reach quickly exceeded their grasp.  This is compounded by untrained human psychological responses to stress and fear.  Some of the lethal gotchas I’ve seen are inability to understand aerodynamic concepts like stall speed to load factor, density altitude, aircraft system interactions, emergency procedures, operation in adverse weather or IMC, jet engine thrust response time to throttle commands, etc.  You also have the unusual quirks specific to each aircraft.  The F-16, for instance, can enter a deep stalled condition lethal at low altitudes if not properly flown.  These kinds of phenomena exist on other fighters with neutral or negative dynamic stability as well.
The exact cause of the accident in question is not totally clear, so anything specifics would be speculative.  If someone can find the Norwegian AF accident investigation report on this, we can read it and see what their conclusions were.

From the news story itself:  an air force lieutenant colonel said

They know how to start the motors to check them and can maybe even taxi, but they don’t have a chance after takeoff ... fighter pilot training lasts more than two years and that it is madness for untrained personnel to try flying an F-16.

That suggests not suicide but sheer luck with the takeoff, which luck then ran out.  Exactly how it ran out may be impossible to determine from what little evidence remained after the crash.

"That suggests not suicide but sheer luck with the takeoff" It may have been sheer luck with the take-off, but that isn't to say that the whole exercise wasn't (intentional) suicide.

Speaking beyond my expertise (and veering off topic), someone with that intention could have finished the flight more dramatically.  Maybe they tried...

I think when someone without training steals an airplane they probably have a low survival expectation...

@CamilleGoudeseune They could have, but a majority of people who set out to end it all, don't necessarily want to take the world with them, stealing a fighter jet and managing to just kill yourself (and a barn), along with $15 million of government property is pretty dramatic compared to most others.

Speculating on motives and choises suicidal people make is rather, well, pointless. A person who has decided to take ones life acts beyond reason, as we have seen in the case of the very sad Germanwings crash. When you no longer have the will to live, all bets are off.


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Determine Vx and Vy from other climbing rate datas
I am developing a small program, working with Microsoft Flight Simulator 2020. For now, I can show my takeoff graph which display the altitude on the y axis and the distance in x axis. I would like to add Vx and Vy curve on this chart but I can find an easy way to determine these curves with the data I have.
So my question :
Based on my actual indicated speed and climbing rate. If I know that my Vx speed is, let's say 55kt, how can I find the corresponding climbing rate ?
More precisely, if (at full power) :
Vi=62kt => climbing rate is 750ft/min (data that I know)
So :
Vx = 55kt => climbing rate is  ????
Vy = 70kt => climbing rate is ???
I know there is some formulas including weight, drag, etc.. but is there a way to find the climbing rate Vx, Vy with already a Vi/climbing rate relation that I know like above ?
I'm sure there's a way to find it but I'm stuck.
Thank you a lot for your information.

I don't think you should be looking at a formula to accurately calculate Vx/Vy. The CFD involved is non-trivial. You probably want to find a chart that you can export into a table, like a 2D array and use that as a lookup table in your program. With that you can obtain a particular Vy given some Vx. This obviously requires a specific table for each aircraft.

Related to my first comment: Have you checked the SDK for MSF2020, if it already exposes this sort of functionality for you, for each aircraft? That might be ideal for you.

Thank you for your response, Actually there's some variable related to that. but it's just a some speed values in knots like Vx or Vy, so impossible for me to draw a graph with that, I need a climbing rate to build. I will re-explore the sdk anyway. Thank you

Since you have only one data point and no other information about the airplane, it is impossible to calculate the climb rates exactly. It seems your data point is neither at best climb angle nor best climb rate, but somewhere in between. Since the climb speed at both points is not so different, the climb speed at your in-between point should already be close to the desired values.
Now I have to guess: Your airplane is piston-powered, with a propeller. Next, I assume a constant speed propeller. The general behavior of thrust and drag over speed will then look like in the diagram below, which is for a generic propeller airplane. Change the numbers on the axes, and it will describe your airplane well:

The best climb angle is achieved close to stall speed and the highest rate of climb at half way to the point of best L/D. To see the formulas for calculating both speeds see this rsp. this answer. With your one data point and the shallow gradient of the climb rate over speed curve, I would expect that your best rate of climb is only a few percent better than the 750 ft/min at 62 kts and your best angle climb speed a few percent below. Since we are missing essential information like power setting, wing aspect ratio and zero-lift drag (fixed gear or not?), any further speculation will stand on very weak feet.

Thank you a lot for you information and this diagram, that helps me in my project

@Thibaultblf That's the idea of this site. If you know more about your plane, I can maybe get more precise with the answer.

While there may be only a few degrees difference in angle of climb between Vx and Vy, let's see what those few degrees mean.
The easiest way to determine climb rate at Vx and Vy is to actually fly it.
However, fairly accurate mathematical approximations of rate of climb may be made if one knows the angle of climb and the airspeed, simply as sine $\theta$ × airspeed
If climb angle is unknown, one may derive an angle of climb by calculating excess thrust at Vx and Vy, and building a trigonometric function vs the weight of the aircraft.  Note that there is more excess thrust at Vx, allowing for higher angle of climb, but the aircraft is aerodynamicly "cleaner" at Vy, allowing for more efficient use of thrust.
The result is a lower angle of climb at Vy, but a greater rate of climb.


text:
Are flaps a good idea for airfoils with a lot of camber?
I have a wing with an airfoil s1223 which is an airfoil with a lot of camber. the take off distance is limited so I want to implement flaps for this issue but I have the doubt if this is a good idea.

What is the application?  The S1223 is a very thick, heavily cambered airfoil.  Does your aircraft cruise at more than 60 knots?  How slow do you want to fly?  You may try airfoil tools and look for an even thicker, more heavily cambered airfoil, and see if you can add in slats and flaps for better short field performance.  Note on the polars, these wings start lifting at negative AOA.

The S1223 airfoil is very similar to a birds wing and is already designed (and limited) to low speed flight.  Heavily undercambered wings were popular in the early days of flight as they offered high lift at low speeds. Modern airliners still use this configuration to land at 1/3 their cruising speed.  However, as speed increases, this configuration is very draggy.  This is why airliners "fold up" and decamber to cruise.  Towards the 1920s designers began to reduce camber, particularly undercamber, with thinner wings and a "straight across" bottom.
So to improve your short field take off distance, the list as follows.

More power.  A larger engine can accelerate the aircraft to flying speed faster.
Bigger wing.  Same design, just bigger.
Lower aspect ratio.  Surprisingly, lower aspect wings, though less efficient, stall at lower
  airspeed.
End capping your wing tips.  This helps maintain higher air pressure under the wing.
Slotted full span flaps or flaperons, found on Ju-52 "doppel wing".  Ancestor of Fowler
  flaps.  May be better than simple flaps for heavily undercambered wing.
Slats and flaps together.  Produce the highest possible Lift coefficient.
Ask Peter Kampf, he always has some good ideas.

Flaps generally help with short field take-off distance, but you should check the takeoff performance charts in the POH to understand your aircraft's limits and the effect of flaps.

Flaps generally increase field performance (lower speed ok for same weight), but reduce climb performance (higher drag for same lift).

Good point.  I edited my answer to be specific to "short field take off distance".


text:
For IFR flights that require two alternates, is there a regulation that requires enough fuel to reach the furthest one?
For flights that have two alternate destinations, I'm looking for a reference - either EASA or ICAO - that states that you need enough fuel to reach whichever alternate would require the most fuel to get to.
I think this is common sense, but I need a reference if anyone has it?

EASA OPS 1.255, appendix 1, 1.4 b).
I don't have the text in English here, sorry.

1.255 points to “(D) Fuel to reach the destination alternate via the destination, if a destination alternate is required; and”. I read the question as when 2 alternates are required.


text:
How does vorticity change the lift coefficient of an airfoil?
For airfoils in unsteady motion, the lift coefficient oscillates and the wake is characterized by vortex shedding.
How does vortex shedding affect the lift coefficient for an airfoil?

Shed vortices from unsteady flow over an airfoil result in decrease and phase lag in lift.

Ref: https://www.researchgate.net/figure/Vortex-shedding-from-an-airfoil-oscillating-in-pure-heave-2_fig2_251006855
Using thin airfoil theory in incompressible flow, the lift coefficient for an airfoil undergoing cyclical pitching and/or heaving can be expressed as (Ref. Drela, Flight Vehicle Aerodynamics):
$$C_l=\text{Re}\{ C(k)C_{l_Q} + C_{l_A} \} + C_{l_0}$$
$C_{l_Q}$ is the circulatory part of the lift, which, at steady-state, is equal to $2\pi\alpha$. $C_{l_A}$ is the non-circulatory part that have to do with fluid inertia; at steady-state, its contribution would be zero. The last term is the camber contribution. $C(k)$ is the Theodorsen function, which serves as a complex gain on the circulatory part of the lift. $\text{Re}$ here refers to the real-part of the function, not Reynolds number.
The decrease in lift and lag is readily seen in the Theodorsen function, where $C(k)=F(k)+iG(k)$:

Ref: https://pdfs.semanticscholar.org/8457/c72b980f2f129a9f211617a5cdee4e162b75.pdf
The reduced frequency, $k=\frac{\omega c}{2V_\infty}$, denotes how many airfoil chord lengths per flow distance traveled in one motion period ($\omega$ is the angular frequency of the cyclic motion), and is a measure of how much the cyclical motion affects the flow on the airfoil. As $k \to 0$, there is no attenuation in lift and no phase lag; this is the quasi-steady aerodynamics. As $k$ increases, there is increasing attenuation in lift, up to 50%. The maximum phase lag occurs at $k \approx 0.25$.
For most rigid-body motions in commercial aircraft, the reduced frequency is low and the quasi-steady assumption is valid.

Thanks. in the formula of $C_l$ it is not clear, is that a multiplication between Reynolds number and the other coefficients? $C(k)$ is a complex number, so the $C_l$ is a complex number? how to read that graph of theoderson function?

@IamNotaMathematician Re here refers to the real-part of the overall complex function, thereby making Cl real. The graph shows the real and imaginary components (corresponding to the blue line parametrized by k). The arrow shows the phase.

Ah thanks for clarifying, Just a last question: what is the phase?

@IamNotaMathematician What do you mean "the phase"? What is phase? Phase is the angular lag. https://en.wikipedia.org/wiki/Phase_(waves)

Yes I know what it is, but in this context, I have no idea what does this mean "phase lag in lift" how ? with respect to what?

@IamNotaMathematician With respect to the cyclical motion, as explained in the second paragraph.


text:
How do viscous drag and form drag individually change as a function of angle of attack?
Typically, when dealing with airfoils, the drag coefficient $C_d$ is given as a function of angle of attack. If we limit the discussion to 2D subsonic incompressible flows, then the drag is the sum of the viscous drag and the form drag (pressure drag), equivalently:
$$C_d = C_{d,\text{visc}} + C_{d_,\text{form}}$$
Where: $C_{d,\text{visc}}$ is the viscous drag coefficient, and $C_{d_,\text{form}}$ is the form drag coefficient.
I've never seen, these coefficient plotted as function of angle of attack individually. That is, $C_{d,\text{visc}}=f(\alpha)$, or $C_{d_,\text{form}} = f(\alpha)$.
The reason I want to see them plotted individually, is to emphasize the contribution of each type of drag (qualitatively, I know that for angles of attack below stall, the viscous drag is higher than form drag, but for angles beyond the stall, (boundary layer separation), the form drag dominates).
Are there any graphs showing these coefficients individually, say for NACA airfoils?

do u want a graph all the way up to 90 degrees or just stall?

Viscous drag probably won't change much if you don't change configuration, but considering form drag is very good.  This would be part of induced drag (making lift).  Interestingly, form drag also comes into play when one uses excess lift as a propeller.

@Abdullah: I think up to 30 degrees will be sufficient.

Wind tunnels are stingy with the data they reveal. They only give the total value but not neatly split into its contributions. Therefore, any such table needs to be calculated.
Since XFOIL, which is now around for more that 30 years, we have such a tool and it does output the single contributions. However, I know of no publicly available collection which lists those drag components for a range of airfoils. And since XFOIL becomes unreliable with larger flow separation, the data is only valid for attached flow and maybe a bit beyond. But certainly not up to 30°.
In Xfoil, load an airfoil and enter OPER. Compute the desired point and switch into VPLO. There you can plot the skin friction coefficient with the CF command. In order to extract its numerical value, toggle the PACC switch in OPER and save a range of points to file. In the file you will find to the right of the CD column one labeled CDp. This is the pressure part of the drag. Use a tabulation software of your choice to calculate the difference between CD and CDp: This should be the friction part of the drag coefficient.

Actually, for angles below stall, one can compute both components. Using pressure integration to compute the form drag, and the wake rake technique or force balance to compute the total drag.

Could you please elaborate a little bit on how to get each contribution from XFOIL, I can't find about that. Thanks

@Navaro Using pressure integration is highly unreliable for computing form drag. You're much better of computing the shear stresses for viscous drag, then computing the total drag from far field momentum defect, then computing the difference for pressure/form drag.

@IamNotaMathematician: I added a new paragraph to the answer. Comments are poor for explaining this.


text:
Are VOR airways being replaced by RNAV routes as VORs are decommissioned?
I understand that VORs in the US and elsewhere are being removed from service gradually. The FAA plans to maintain a Minimum Operational Network, but still I imagine many VOR airways will also have to be removed when their respective VORs are shut down.
Is there any indication that the old VOR routes will be replaced by RNAV routes (Q and T routes)? Or will the VOR airways be removed without replacement, leaving pilots to file direct routes instead of using published routes?

It's fascinating comparing charts on skyvector.com for Canada around Montreal (where there a lot of T routes) with the south shore of Lake Erie where there's a giant hole with no airways. It seems useful to have T routes where there'd be a lower MEA than the surrounding OROCA, but I suppose in many parts of the US the difference between the OROCA and MEA is negligible.

Short answer: there seems to be no general plan to replace airways with Q and T routes. The FAA originally proposed replacing them, but the final rule doesn't include it.

You can review the source rulemaking documents in the Federal Register and it looks like the idea of replacing (or retaining) airways seems to have been discarded, possibly in response to comments.
The initial notice suggests that the idea was indeed to replace the airways:

Existing airways, routes, and procedures eventually would be replaced
by RNAV Q (high) and T (low) Routes, and RNAV STARs and DPs.

The proposed rule got some negative feedback on the T and Q route idea from two major industry lobbies:

Comment #20: AOPA and the National Business Aviation Association (NBAA) both expressed support for direct routing and avoiding
excessive implementation of additional T and Q routes.
FAA Response: In the NextGen environment, T and Q routes increase capacity and efficiency while maintaining safety by minimizing impact
to air traffic control. T and Q routes allow controllers to safely
manage air traffic during peak periods and to ensure predictable
transitions between busy traffic areas. T and Q routes overlaid on
existing airways defined by VORs could mitigate potential impacts to
the discontinuance of VOR navigation services.

The final rule has only one mention of airways, and doesn't mention T and Q routes at all:

Retain most VORs in the Western U.S. Mountainous Area (WUSMA),
specifically those anchoring Victor airways through high elevation
terrain.

My reading of all that is that the FAA originally intended to move airways to Q and T routes, but dropped the idea after receiving feedback. Or perhaps they just floated the idea to see what the reaction would be.

Thanks for the info! I wonder how controllers feel about removing routes and using more direct routing. Would widespread adoption of this plan increase their workload significantly?

@asb1230 This question might have some more info about that, or you could ask it as a new question. "Direct" doesn't mean that every aircraft will literally fly directly from A to B, ATC will still assign routes between waypoints for safety and traffic management.

A couple of years ago a black hole appeared over Austria (Vienna FIR—LOVV; except west Tirol which is very narrow and routes are still used in the neighbouring FIRs) where there are no routes any more and all routing is ad-hoc between fixes.
It has since grown to cover Slovakia (Bratislava FIR—LZBB), Hungaria (Budapest FIR—LHCC), Slovenia (Ljubljana FIR—LJLA), Croatia (Zagreb FIR—LDZO), Serbia + Montenegro (Belegrade FIR—LYBA), Bosnia and Herzegovina (Sarajevo FIR—LQSB), Albania (Tirana FIR—LAAA), and North Macedonia (Skopje FIR—LWSS), though most of these have only removed high-altitude routes and still keep some low-altitude ones.
There is also a new one over Ireland (Shannon FIR/UIR—EISN), which also only keeps a few low-altitude routes.
I have no idea what the plan is in US, but it can be expected that more FIRs will join this movement to just use ad-hoc routing between fixes (provided they have the radar/ADS-B/ADS-C coverage it requires).


text:
Is it mandatory to go missed following full scale CDI deflection?
In the USA, AIM 5-5-5 paragraph a1 specifies when a missed approach is required. I have also heard that a missed approach is required if the aircraft reaches full scale CDI deflection on a localizer course (this old CFI test standards doc from 2001 says it’s recommended in paragraph b).
Where is this requirement written? Is it true for all types of approaches, or only ILS and LOC?

The point being, once you've reached a full scale deviation in IMC, there's no telling how much beyond it the airplane has gone. Your USA AIM 5-5-5 is quoted here, and point 'b' is sufficient to conclude an immediate Missed Approach:

5-5-5. Missed Approach
a. Pilot.
1. Executes a missed approach when one of the following conditions exist:

(b) Determines that a safe approach or landing is not possible.

With a full scale deviation and the LOC beam narrowing as you approach the RWY, what is the pilot going to steer at low altitude and descending lower in IMC? What is the IFR reference that the pilot would use? A VOR course? An FMC course? A locator beacon (NDB)? Even if these existed, there would have to be an IFR procedure to continue to landing, including revised minimums.
Quoted below are the Elements of a Stabilised Approach, widely accepted as The Gospel by regulators and industry, All manufacturers have incorporated into their procedures, this concept from the Flight Safety Foundation's ALAR 'toolkit':
(ALAR = Approach and Landing Accident Reduction )
(notice too, the applicability to VMC conditions)

Most airlines and other aviation organisations specify minimum acceptable criteria for the continuation of an approach to land. These vary in detail but the following summary published by the Flight Safety Foundation is one view of the important considerations.

Their Approach-and-landing Accident Reduction (ALAR) Briefing Note 7-1 suggests that "all flights must be stabilised by 1000 feet above airport elevation in IMC and 500 feet above airport elevation in VMC. An approach is stabilised when all of the following criteria are met:

The aircraft is on the correct flight path
Only small changes in heading/pitch are necessary to maintain the correct flight path
The airspeed is not more than VREF + 20kts indicated speed and not less than VREF
The aircraft is in the correct landing configuration
Sink rate is no greater than 1000 feet/minute; if an approach requires a sink rate greater than 1000 feet/minute a special briefing should be conducted
Power setting is appropriate for the aircraft configuration and is not below the minimum power for the approach as defined by the operating manual
All briefings and checklists have been conducted
Specific types of approach are stabilized if they also fulfil the following:
ILS approaches must be flown within one dot of the glide-slope and localizer
a Category II or III approach must be flown within the expanded localizer band
during a circling approach wings should be level on final when the aircraft reaches 300 feet above airport elevation; and,
Unique approach conditions or abnormal conditions requiring a deviation from the above elements of a stabilized approach require a special briefing.

An approach that becomes unstabilised below 1000 feet above airport elevation in IMC or 500 feet above airport elevation in VMC requires an immediate go-around.

This is interesting information, but it does not address whether this is a mandatory requirement by the FAA, and if so where it is written

I don't think there is a law or regulation that specifies that because it's more of an airmanship issue.  Operators will have a requirement in their SOPs however.   This is a good example of that sort of thing taken to an extreme https://en.wikipedia.org/wiki/First_Air_Flight_6560.

Imagine toodling along being beyond the full deviation at low altitude, blind in IMC. As the person in-charge in the cockpit, I don't think that's an acceptable situation.

Well, this would highly depend on when the CDI went to full scale deflection. I would imagine that it would not do this before the minimums. Probably not even before the VDP or even the AER. But, it definitely would for a circling approach. But, that is academic and does not address the actual question posed.

Ironically, I'd edited out the following to make the answer less complex: "Making it more difficult to estimate the deviation is the fact that ILS LOC full scale is normally referenced to the lateral edges of the RWY at the landing Threshold. Thus it varies with RWY length ie, a long RWY has a narrower LOC beam than a short RWY."

I agree with skipper44's interpretation of the maneuvers for a safe landing being the broad reasoning that if you dont know how far off course you are you cant make a safe landing. I did some more digging and Ill present another option from the FAA that might also satisfy the question.
According to 14 CFR § 91.181 - Course to be flown when operating under IFR you need to be "on course"

§ 91.181 Course to be flown. Unless otherwise authorized by ATC, no
person may operate an aircraft within controlled airspace under IFR
except as follows:
(a) On an ATS route, along the centerline of that airway.
(b) On any other route, along the direct course between the
navigational aids or fixes defining that route. However, this section
does not prohibit maneuvering the aircraft to pass well clear of other
air traffic or the maneuvering of the aircraft in VFR conditions to
clear the intended flight path both before and during climb or
descent.

Now if we dig into order 6750-16E which lays out the spec for designing ILS systems we can see that the all CDI's must be calibrated to 150 micro amps equals a full deflection and likewise this needs to be calibrated to the edge of the ILS course (bolded for emphasis)

c. Localizer Receiving Equipment. The localizer receiving equipment
generates a meter deflection indication, which corresponds to
differences in depth of modulation. When the aircraft is on course
there will be a zero-centered meter. When the aircraft is left side of
the course, the Course Deviation Indicator (CDI) needle will deflect
to the right and when the aircraft is right side of the course, the
needle deflects to the left. The CDI is calibrated so that 150 micro
amps (.155DDM) represent full-scale deflection on each side of the
course centerline. The angular value corresponding to the 150-0-150-
micro amp values is defined as the course width. The standard or
“tailored” course width provides for 700 feet between the full-scale
deflection points at the runway threshold. When the localizer antenna
to threshold distance is less than 6678 feet, the course width is
capped at a maximum of 6.0 degree. Localizers used for Category I
service only may be “non-tailored” if necessary within the limits of
6.0 degrees maximum and 400 feet at threshold minimum. Localizers supporting Category II/III service must be “tailored.”

As such I would say that if your needle goes full deflection you are no longer on course and thus no longer legal under 91.181 and dont know how far you are from the course anymore so you have no way to know how to intercept it (even if you practically know where it is) but going missed allows you to easily establish yourself on the missed course (if you have two CDI's your likely tuned in already anyway or should be)

Interesting info on localizer equipment. FAR 91.181 is interesting... victor airways for instance are 8 miles wide. If I’m not on the centerline of the airway but a mile to one side, am I operating illegally?

It'd be interesting to know how to maintain a lateral (say 1 nm) deviation from a "victor" airway centerline using VOR radials? A  victor-AWY segment vs descent close to the ground on a narrowing ILS beam is not the best comparison. However, the 8 mile figure says it all, 1 nm off the required Track would not be a violation. But, if you do not, or cannot return to the radial, it would warrant giving a shout to ATC. Modern PBN routes, very explicitly define their 95% containment figures as RNP.  A  1nm deviation would not be illegal on a RNP1 ARR, but it would be on an RNP 0.3nm Approach.

The FAA Airman Certification Standards (available here) for the instrument rating require the following:
"The standard is to allow no more than a 3⁄4 scale deflection of either the vertical or lateral deviation indications during the final approach."
From a purely legalistic point of view, not performing to this standard would invalidate an instrument rating.
But far more practically: it's dangerous! Radio beams are not perfectly accurate, nor are receivers.
For comparison, the UK Flight Examiner's handbook CAA link here requires applicants for commercial or higher license to not exceed half-scale deflection.

I'm not sure what you mean by "not performing to this standard would invalidate an instrument rating"?

@Pondlife The ACS specify the skills required for the instrument rating. Full-deflection (on an instrument approach, with due regard to relevant circumstances) would not be consistent with those requirements.

Right, if you don't fly to ACS standards then you won't pass an instrument checkride or IPC. I guess when I hear "invalidate" it sounds more like losing your instrument rating if you don't fly to those standards in general.

I believe the Standard applies regardless. On a checkride, the result might be a Notice of Disapproval. Out in real life, the result might be FAA Certificate Action. From their website: "Suspensions of indefinite duration are issued to prevent a certificate holder from exercising the privileges of a certificate pending demonstration that the certificate holder meets the standards required to hold its certificate."
But this is getting very legal. I think the original poster  was looking for information useful in decision-making. ;-)


text:
What is the indicated device under the tail of this B-29?
Was lucky enough to have the B-29 "Doc" flying over the house this weekend.
What's the mechanism under the tail indicated by the red arrow? Tail-strike preventer?
I did some searching and found it in other pictures, but never a labeled diagram.

(Personal photograph)

Its a "tail bumper":

Source: Fiddlersgreen.net
Because the B-29 is so long, it helps prevent tail scrapes when taking off/landing.
Here is a close-up picture of the one on "FiFi":

Source: Airport-data.com

Great pictures, thanks.

The OP might be interested to know that Concorde also had one, for the same reason.  Details of Concorde's landing gear.

Tail skids/bumpers (albeit not nearly as prominent as the ones depicted here) are common on long-bodied airliners (everything from Dash 8-Q400s to B787-10s)

@Graham thanks! I'll be lost in that website for a while. Wow.

I believe the B-25 has a fixed one.

Huh. I would have assumed it was an antenna. TIL, I guess.

Is there a wheel or something that attaches? It looks to me just like it scrapes along the ground.

@BruceWayne that's correct, it's a skid, not a wheel. If you hit it, your take off technique needs work.

@RonBeyer aha! Thanks for that simple clarification. I am (obviously) not a pilot and thought since the planes were so long it typically skids just enough to need a "tail bumper" for the last touch before taking off. Now I get it - you never want to use it, but it's there just in case.


text:
What is this (possible) small jet trainer?
Photographed just now (10/18/2023) near Ellington Field, Texas.
Hunting around on some aircraft pages didn't turn up a match.
I bumped the contrast up to see features better.

Looks like a BAE Systems Hawk...  https://en.wikipedia.org/wiki/BAE_Systems_Hawk

Indeed! Thanks. New yard bird.

That appears to be correct based on FlightRadar24 history.

This is a BAE Systems Hawk Mk 67, one of twenty formerly operated by the South Korean Air Force. It still retains the South Korean camouflage scheme. However, Korea retired its Hawks in 2013, and this Hawk is now privately owned by RAVN Aerospace, based in Houston, Texas.
RAVN have painted their company logo (which I'm guessing is a raven that thinks it's a bird of prey) on the tail, which you can just about make out in your picture.
source
They appear to own at least four of these ex-Korean aircraft.

Wishing there were an extra +1 available for the description "a raven that thinks it's a bird of prey" - very nice!


text:
Why don't turbofan engines have shrouds affixed to the fan blades?
For a turbofan to be efficient the gap between the blades and the shroud has to be extremely small. Why don't we just attach the shroud directly to the blades and let it spin as one? Would that decrease the efficiency of the fan or is it just not structurally sound?

This has actually been done, at least on the CFM-56 series at some point.

The image is taken from here, the article is about the F108 engine which is the US military version of the CFM-56.
In newer versions of the engine the blade-tip shrouds have been replaced by mid-span shrouds as below (from Wikipedia), or have been removed.

As pointed out by Camille Goudeseune, turbofans have to accomodate a lot of situations, and a blade-tip shroud adds a lot of mass and therefore increases loads in the blade, further reducing fatigue life.
Among the advantages of this configuration that were not mentioned in the question or in the other answer is that shrouds help reduce vibration amplitudes through frictional damping. This explains why mid-span shrouds are still in play in several engines, while these do not participate in reducing blade-tip losses.
Finally, while this configuration is seemingly not used anymore on fan blades, it is still used in other parts of modern engines, specifically the turbine module.
As an example, the picture below is from the GE9X website, see the Low Pressure Turbine blades.

To add to the fine answers:
The rotating shroud woud add extra mass, as the duct would still have to run past it. This mass would also be rotating at high speed, creating substantial gyroscopic forces, and on top of all that, making the engine less responsive.
Then there are the constructional issues: although not at all impossible to engineer, as there are some implementations, the structure would not be as simple as one might think. High rotational speeds, bending of blades, vibrations etc would have to be taken into account and dealt with. Balancing a huge rotating disk would definitely be a pita. there is a Q&A somewhere here about balancing fan blades, I'll try to remember and find it and add it here: adding a disk around the blades would not make the equation simpler. A wide operational temperature  range does not help either. We are talking maybe from + 60° C all the way down to - 70°C
All in all, there is a lot of dynamics involved with fan blades, best keep the construction as simple as possible.

Land-based turbines sometimes use rotating shrouds, with something like a https://en.wikipedia.org/wiki/Labyrinth_seal to reduce leakage. So it's structurally sound in principle.
But turbines in airplanes have to tolerate nonaxial loads, foreign object ingestion, and a broad range of ambient temperature, pressure, and humidity.  Affixing the blade tips to the shroud may not tolerate such abuse well, in terms of not exploding, or surviving the next hour, or lengthening the interval between engine overhauls.  Better to bang up a few blades than to lose the whole rotor.  That would outweigh even a few per cent improved fuel efficiency.


text:
Is there a limit to a subsonic ramjet's pressure ratio?
Subsonic ramjets have high specific fuel consumption. This indicates to me they must have a low pressure ratio.
Is there a limit to how high pressure ratio one can achieve with subsonic air? Why can't you just increase the area ratio between inlet and the diffuser exit?

Yes, they have a limit at around 2. And this can only be achieved at Mach 1, as Peter Kampf points out. Increasing the inlet to diffuser area ratio to extreme values will just lead to your engine being filled with slow moving air. The mass and volume of air in your engine will increase, but neither the pressure nor the rate of airflow will increase appreciably

And that limit is only possible at Mach 1. At a slower speed the pressure ratio will become even lower.

which equation is this deducible from?

@FrancisL. there you go


text:
What is the general process for flying a private aircraft to another country?
Let's say I want to fly a private airplane to another country. How does one arrange such a flight? Of course this might vary between states, but in general do you need a special permit to fly in with a particular airplane, other than a permit to enter the country? Do you schedule a landing with the airport of destination?

Are you asking as a passenger, or a pilot?

As a pilot; I'll edit the question

It really depends on the laws of the country you are planning to flight to.
If you want to fly between states in the US, there is no requirement to do any paperwork. Federal Aviation Regulations allow you to fly any distance domestically without filing a flight plan, assuming you are flying under visual flight rule (don't need ATC service), and don't need to fly through any restricted airspaces (most of the US airspace isn't restricted).
Canadian laws require flight plans for all flights longer than 25 nautical miles. However, filing a flight plan doesn't necessarily involve paperwork. Most people do it over the phone.
Flying in Western Europe is similar, but since most airports in Europe require advanced notice (and payment of a landing fee), you'll also have to call the destination airport. Technically you can still fly anywhere you want without doing that... you just won't be able to land.
I don't know much about flying in Eastern Europe, Middle East, or Asia, though if you are in a place like China, where the entire national airspace is restricted and you need a clearance from the military for every take-off... I am guessing there will be paperwork involved.
If you are flying between US/Canada/Mexico, in addition to filing a flight plan (5-10 minutes), you'll also need to notify customs of the destination country so they can expect your arrival to clear you. That also just takes a short phone call.
If you are flying in/out of the US, you'll also need to file eAPIS (electronic advance passenger information system) online. Basically just have to give them names, day of birth, and passport numbers of everyone on the flight, and they will email you a preliminary clearance. You still have to clear customs normally once you land.

Technically some domestic flights do require flight plans... flight in the DC SFRA requires a flight plan; to fly from CONUS to Alaska, you must fly through Canadian airspace and thus have a flight plan. To fly from North America to Hawaii or Puerto Rico, you must fly through an ADIZ and have a flight plan.


text:
Is it possible to make an analogy between a lever and an airplane wing in terms of force applied over distance?
On most aircraft the engine force (thrust) is lower than the weight. Since wings therefore are always capable of generating greater force (lift) than the engine, there is an analogy between an airplane and a lever.
Now, a lever produces greater force by doing the same work on a shorter path. How can we prove that wings enable the doing of work on a shorter path than the engine thrust? Is it reasonable to say the path on which the thrust does the work is the distance the aircraft needs to accelerate to takeoff speed, and the work/energy accumulated this way is used by the wings to exert greater force on a shorter path on the air? (And then this kinetic energy is constantly replenished by the engine keeping it constant, assuming no further acceleration?)
Is this the right Newtonian explanation of flight? How can I find the distance on which the force is doing work on the air?

While this may not answer directly, indeed "lever effect" is used on an airplane. The reason the tail (elevators and rudder) and the ailerons are located far from the aerodynamic center is to have a larger torque, and generate control forces with as little lift as possible (because generating lift also creates fuel-expensive induced drag in proportion).

Well, they call them air PLANES for some reason.  Maybe not a lever, how about a ramp?
How does 1/4th the thrust lift a given weight?  One consideration that is very important for aviators is to realize the best way to use thrust is to create speed.  Speed creates lift.
It is indeed a minor miracle that the airflow over a wing at flying speed creates so much upward force.  One way to see how this works is to look at the back of a boat while it is travelling slowly.  See the swirls and eddies of the water in the wake.  Now speed up and the water separates from the stern and forms a wave behind the boat. The lack of water at the stern is the same as air being deflected away from the top of the wing at sufficient speed.
This area of lower pressure near the wing is lift.  How much to lift a one ton Cessna? The wing is roughly 5 x 40 = 200 square feet.  200 square feet x 144 square inches/square feet = 28800 square inches.  2000 pounds/28800 square inches = 0.07 psi.  Not much, but it works!
Slow down and the wave collapses back to the boat.  This is a stall on a wing.  So lift is INDIRECTLY produced from thrust by forward motion (and angle of attack).

I will note deflection of air off the bottom of the wing also contributes to lift.

A lever is a very poor analogy to a wing. And so is a ramp.
A lever used to lift a heavy load exchanges a small force over a large distance for a large force over a small distance. In both cases the work done (force x distance) is the same. Ignoring friction, a lever is 100% efficient, because the work out is the same as the work put in.
A ramp lifts a weight a short distance against gravity while moving it a large horizontal distance.
However the thing to note about a wing is that (at least in horizontal flight) it's doing no work against gravity at all - because the airplane isn't going up or down.
The wing is doing the same amount of work as my chair (as I sit in it) and a hook while it holds my coat off the floor, neither of which require any energy input - that is, zero work.
A wing is effective at providing a vertical FORCE in exchange for a horizontal amount of WORK. Since no actual work is being done in the vertical direction in level flight the wing has an efficiency of zero %.
It would be nice to understand a wing as a kind of lever, but I'm afraid that's not what it is.

This is the fallacy of work = force x  distance/time.  These definitions were made at a time when work was defined as moving from point A to B.  This would be better defined as Sum of Forces (3 dimensionally to determine direction, average velocity to determine distance).  Much easier to consider forces.  The wing DOES require energy input, in straight and level flight it is in EQUILIBRIUM with GRAVITY (two opposing forces cancel).

@RobertDiGiovanni Work is defined the same way it always has been, which is work = force x distance. The quantity (force x distance)/time is power, and the "sum of forces" is the net force. All Capt. Aerodynamics is doing is explaining that work is perhaps not the right quantity to be focusing on.

I don't think you can make a really useful comparison because the lever is applying force to one fixed object, pivoting around another fixed object, with a fixed mass and a fixed force and you can repeat the same result over and over.  The airplane is applying force to a fluid (gas), which imparts a gazillion variables to an action/reaction situation.
On top of that, the airplane is accelerating a gas rearward to create the forward momentum, and then the wing is taking the same gas and accelerating it downward to create the lifting force, so you have a gazillion variables multiplied by a gazillion variables, which results, if my math is correct, in a jazillion variables.  You get the idea.


text:
What was the first Russian jet designed with the use of area rule?
What was the first Russian jet designed with the use of area rule? Also, how did the Russians acquire the knowledge of this design method? Was Whitcomb's discovery public?

Hard to say with any certainty, but Tu-16 and Tu-95 carry obvious signs of application of the area rule. Both had first flight in 1952, which makes it earlier than the Whitcomb's publication.
Whitcomb may have discovered the rule independently, but Germans knew it since 1940s, so my guess is that the Russians either found it from them (lots of very valuable aerodynamic research data was captured after the war), or developed independently (Russians had/have their own NACA, after all).

I think you're mistaking the pinched in look created by the curve of the wing meeting the curve of the fuselage as an actual coke bottle shaped fuselage.  The TU95's fuselage, being based on the B-29, is just a straight tube.  The earliest Soviet fighter that looks like it's applying area rule that I can find is the Mig 21 where it looks like the turtle deck cross section was adjusted in accordance with AR.  The coke bottle fuselage shape was a band aid solution for airplanes not designed for it (like the F 102 before it became the F 106).  The F4, designed for AR, u can't tell looking at it.

A propeller based aircraft wouldn't benefit from the Area Rule, anyway.

@JohnK, for Tu-95, it's not the fuselage, it's the inner engine pods. And its fuselage is certainly not derived from B-29 (unless you count gaining the knowledge replicating it into Tu-4). On the contrary, MiG-21 is somewhat famous for disregarding the area rule; in its case it's definitely just an illusion from the wing/fuselage joint.

@Davidw, a typical propeller-based aircraft wouldn't benefit from a highly swept wing either. Tu-95 is unique. Its maximum speed is faster than that of many jets.

Actually, Whitcomb formulated "his" area rule after hearing a talk by Alfred Busemann on transsonic aerodynamics. Busemann knew of the work done by the Junkers aerodynamicists and explained the concept without using the name. All Whitcomb did was to give it a catchy name that stuck.


text:
Do plug nozzles improve efficiency on lower throttle settings?
Plug nozzles are used to adjust for the overexpansion/underexpansion of the exhaust with altitude. Do they also adjust for overexpansion/underexpansion of the exhaust caused by lowered mass flow experienced at lower throttle settings? Or does throttling not have an effect on the exhaust shape?


text:
What happens to Ryanair aircraft after they leave the airline?
According to the fleet renovation and the short age of all their aircraft (6.5 years), what happens to Ryanair's aircraft after their time in the company? Are there other companies willing to accept Ryanair's aircraft configurations?

We don't know. There's nothing special about Ryanair's 737-800 configuration. Their yet-to-be-built 737 MAX 200, as well as Easyjet's A319s are the ones with an extra exit, which would affect the resale market.

Most of Ryanair's fleets is sold upon delivery and leased back from lessors. The lessors will then lease the aircraft out to another airline for as long as its safe for the aircraft to be flying.
An example for MSN 29921 would be:
EI-CSF    24. May 2000    Ryanair
C-FTCX    28. Mar 2008    CanJet
OK-TSJ    05. May 2015    Travel Service
C-FTCX    05. Nov 2015    CanJet
C-FTCX    04. Dec 2015    Air Transat
SP-ENO    30. May 2016    Enter Air

(planespotters.net)


text:
Do mono spar wings need compression strut(or ribs)?
Loyolksip

Regarding airplane wings, are compression struts needed in a mono spar wing?
Secondly, are anti drag and drag wires needed in a mono spar wings?

The wing in your picture has a tubular spar. In addition, smaller tubes are used at the leading and trailing edge, and one is running diagonally through the inner half to add in-plane bending stiffness.
Tubes have the same stiffness in all directions, so using a tube gives already some in-plane and torsional stiffness. For the outer part of the wing in your picture, this stiffness seems to be sufficient to not use drag or anti-drag wires. Since loads accumulate from tip to root, the root has the highest loading, and here a bracing tube is added in the inner wing so in-plane stiffness and strength are sufficient. I expect that this wing also uses bracing for the out-of-plane loads, and I checked with the manufacturer's home page: Yes, it does.

Kolb Fire Star II side view, from the manufacturer's home page.
The ribs are supplemented by half ribs placed between the full ribs, so the forward part of the airfoil, where more aero loads and more curvature require more support, is adequately shaped and strengthened. The ribs themselves seem also to be made from rather thin tubes, and this being a rectangular wing, need only a single jig to be manufactured. An N-type truss allows the ribs to transmit shear to the spar.
In all, this is a very efficient and pragmatic wing design. There is nothing missing (well, except for the fabric covering, of course)

Will there be any consequence or needed modification if I should replace the tubular spar with an I beam ?@Peter Kämpf

@DavidTeahay: Yes, an I-beam has high stiffness in one and low stiffness in the orthogonal direction. You cannot simply replace one with the other. What is normally done when the spar is an I-beam is to replace the fabric cover with a strong skin over the forward part of the airfoil. This improves torsional and in-plane stiffness, basically turning the forward part of the wing into a tube.

...."to replace the fabric cover with a (strong skin) over the forward part of the airfoil"......will a light slim aluminum sheet do the job of replacing the fabric cover ?

@DavidTeahay: Yes, an thin aluminum sheet is ideal if it has enough support against buckling. In one direction the airfoil curvature helps, but in the other you would be advised to add internal stiffeners (also for the bottom part where I expect to be less curvature). Spanwise L- or Z-stringers plus a few ribs would give the best support.

http://www.military-airshows.co.uk/press15/nam/04.02.15_monosparwing.jpg

http://www.military-airshows.co.uk/press15/nam/04.02.15_monosparwing.jpg               http://www.military-airshows.co.uk/press15/nam/04.02.15_insidethemonosparwing.jpg         This is the wing of Monospar- vh (a vintage airplane)....can false ribs replace stringers? ......bdw you're actually making the goal of building and flying my own ultralight more plausible....so thank you!....@Peter Kämpf

@DavidTeahay: Interesting picture! I have my doubts about the torsional stiffness of this wing (= aileron flutter already at low speed). Unfortunately, I could not find out what aircraft belongs to this wing. That should be a very light aircraft with low power - just what you want to build.This one at least has a D-shaped nose, which could be made from aluminium sheet or plywood.


text:
Where can I get a graph of lift coefficient against AOA for a symmetrical airfoil?
Where can I get get a graph lift coefficient against AOA for a symmetrical airfoil ? I am asking for a source or link to a graph or table of AOA against Cl of any symmetrical airfoil.

Search symmetrical airfoils in Airfoil Tools DB
Quabeck Sailplane 10 as an example

What causes the wiggle in the middle for 2 of the curves?

@CrossRoads Low Reynold's number effects. I'll take those two out and leave the normal looking ones.

Amazing,thanks pilothead


text:
Can this vane prevent/delay wing stall?
Given that a stall results from the airflow over the top of the wing separating from the wing at high angles of attack, would it be possible to prevent, or at least ameliorate, a stall by deflecting the airflow downwards into the "dead zone" behind the wing using a curved/angled vane located just above the leading edge of the wing?
A rough illustration of what I'm thinking about:

Is this structurally viable? And even with the deflected air, would it retain a sufficient velocity to maintain lift anyways? Interesting in theory but I've been doing some work on my own on boundary layer airflow and you'd be surprised how much these surfaces slow down and create secondary flows, which I GUARANTEE you will eliminate effective lift.

Roll back the title if you don't like it.

This is a very good idea and has already been done. It is called a slat and is positioned ahead of the wing where it will do a better job of turning the airflow and not causing the slat to stall, as shown on your diagram. Slats allow a 10-12 degree higher angle of attack before the wing stalls. Fixed versions in this more forward position have lower drag in cruise.

source
The reason a more forward placement is superior can be seen in the streamlines of the airfoil at high AoA. The inlet gap between the slat and wing is located right at the airstream stagnation point. This is where air pressure is greatest, enhancing the operation of the slat.

source

That climb/cruise diagram seems to confuse pitch with AOA. While climbing you would expect a lower AOA than cruise at equal IAS.

@Sanchises The AoA when climbing will be lower that in S&L flight only if the attitude of the plane is kept constant during the climb; but we usually pitch up the plane when climbing, and that increases the AoA significantly...

I mean, constant and the same as when flying S&L... You're flying level, then you open the throttle and keep the attitude constant. You'll climb, and the AoA will decrease... However, you could also pitch the plane up, give more gas and you'll be climbing at the same IAS, but with an increased AoA...

However, you could also pitch the plane up, give more gas and you'll be climbing at the same IAS, but with an increased AoA That's incorrect. In climb, the thrust vector has a vertical component, which reduces the lift required from the wings. At the same IAS, this means a reduced AOA (except during the transition from S&L to climb, but that's only a few seconds) during climb. See also https://aviation.stackexchange.com/a/12720/4108

Also, most large aircraft have them.

@Sanchises Climbing at cruising speed is an enroute activity where changes in AOA are a fraction of a degree. That is not the intent of this diagram. This is from a STOL aircraft manufacturer whose products climb and descend steeply. This type of climb requires power and takeoff speed are low, so there is neither the possibility or desire to climb at cruising speed. Slow takeoff, climb and descent use high AOA to get the necessary lift. The situation is similar for airliners but the climb and cruise speeds are multiplied by some large number. No aircraft takes off or lands at cruising speed.

@Sanchises When climbing with a pitch-up attitude, the AoA is higher the more pronounced that pitch-up attitude is. The fact that the prop thrust may reduce the necessary lift from the wings has nothing to do with the obvious fact that the relative wind strikes the wind at a much higher AoA. That's due to the pitch-up attitude...  I use to fly a 'Savannah' STOL and know that situation first-hand.

I'm just saying that the diagram would be better labelled "high AOA" instead of "climb". Fact is, the "climb" situation in this diagram applies just as well to a short field landing.

@xxavierv That just doesn't make sense. I fully agree if you say the low takeoff speed gives a high AOA, but saying a high pitch attitude results in a high AOA just doesn't add up. Extreme example: what do you think the AOA is in a fully vertical takeoff?

@Sanchises "I'm just saying that the diagram would be better labelled "high AOA" instead of "climb"." I agree. The thing that caused all the comment was the "climb at cruise speed" which is not commonly done. Most aircraft don't have excess power and have to reduce speed (and drag) to get the power to climb. So while your thrust contribution to lift argument is technically possible, the effect for normal aircraft is minuscule even in theory and not achievable in practice due to that power limitation.

@Sanchises You're wrong, probably because you have no flying experience at all. If you could fly a STOL, where these things are more pronounced, and hence more clear, you would perhaps understand them better. But I'm not going to insist. Period.


text:
Are there any passenger aircraft with no cabin access to/from the cockpit?
Most passenger aircraft (airliners and business aircraft) have an internal door or doorway connecting the cockpit area to the main cabin; are there passenger aircraft where there is a solid partition isolating the cockpit from the passenger cabin, and passing between the two requires exiting the aircraft?
Yes, I know that many early passenger aircraft had enclosed cabins with separate, open cockpits; I'm wondering about aircraft with an enclosed cockpit and a separate, enclosed cabin.

Does a Cessna 208 count? Some small operations use aircraft that don't have cockpit doors like the Caravan.

Looking at this photo, it looks like the Caravan's cockpit is merely the front end of the cabin; by "no cockpit door or doorway", I meant the opposite extreme, with no internal access at all between the cockpit area and passenger cabin.  Will edit the question to clarify this.

I don't think anything modern will meet your criteria, however some of the very first passenger planes were pretty much just that, with pilots often still sitting in open-cockpit while passengers where "seated" in the fuselage.

While such a thing could be built, it seems rather impractical. You'd need a separate lavatory for the crew, separate facilities for the crew to get food and drinks, a separate entrance, etc...

@ZachLipton that's a fair point but it could also be argued that the 747 without the staircase would fit that description.

@fooot True, though sacrificing all that premium passenger space (even more on the 747-8) would be a nightmare for airlines and could tip the economics of whether the aircraft even makes sense to fly.

Some DH.83 Fox Moth had an enclosed cockpit (not all, some had open cockpits).
Several examples are still flying, including one in Ottawa.
It has a cabin for three passengers with an entry door, and behind and above that a cockpit with (in some aircraft) a sliding glass canopy
Flying example from Vintage Wings of Canada
Wikipedia page

The only one I can think of is the Junkers F13. It has an open cockpit and an enclosed 6 passenger cabin. There's no access between the two areas; only a small window.

Credit:THOMAS LÜTHI / RIMOWA 2016
The CEO of Remowa is having recreations made of the aircraft which first flew in 1919. It was (according to Rimowa) the world’s first all-metal commercial aircraft.

Nice find, but it has an open cockpit, and the question specifically asks about "aircraft with an enclosed cockpit and a separate, enclosed cabin".  (Italics in original, but bolding added.)

Okay, I may have found one; the Bristol Wayfarer (a passenger version of the Bristol Freighter) had a passenger cabin in the main fuselage, with an enclosed cockpit perched on top.  The aircraft's arrangement makes me suspect that the cockpit was isolated from the main passenger cabin, but I can't confirm yet whether or not that was actually the case.  As @jwenting's comment points out, the Freighter must have had some internal access between the cockpit and cabin, as it doesn't appear to have had any external cockpit access doors (except for a roof escape hatch which was probably not routinely used for non-emergency crew ingress and egress).
There's also the Tu-116, a modified Tu-95 bomber with two passenger cabins mounted in its fuselage where the bomb bay had previously gone, with no internal access between these and the cockpit; two, originally meant to carry Nikita Khrushchev to other countries (although, as it turned out, they never actually carried the Comrade General Secretary), were built, but served only as military transports (so, partial example?).

Really?  Again with the drive-by downvoting?

probably because you don't answer the question, but rather just provide some unfounded speculation. btw, looking at photos of the Bristol 170 it does not appear to have external doors to the cockpit, unless you count the hatch in the roof.

Link to video clip on the Tu-116-- the first aircraft in this video-- https://www.youtube.com/watch?v=xbXURIgfYvc

as far as I know, there is no such aircraft. Simply because it would be very hard to realize. The cockpit is at the very front of the aircraft. Followed by the cabin.
Even large modern cockpits are comparably small and don't offer a lot of space. All modern passenger aircraft are designed in such a way that the front door or doors (if one on each side) are located right BEHIND the cockpit. These doors are also used for the flight crew, to get aboard the plane, passing then through the cockpit door.
Meaning not to have a cockpit door, would mean that the cockpit would have to had its own door, which could only be used by the flight crew to get inside and outside. This would mean a way larger cockpit and would probably not make a lot of sense, given that most aircraft are already pretty scarce when it comes to free space.
The cockpit door of all modern aircraft however, is locked from unauthorized access. We have a switch in the cockpit, where we can put the door into auto, unlocked or locked mode. If unlocked, the door is open. If locked, the door is closed and cannot be opened by anyone. In standard, auto-mode, doors are locked but can be opened by cabin crew, usually by entering a key combination. Also the side cockpit windows can be removed in case of emergency and serve an an emergency exit for the pilots, which is used only by them. To leave the aircraft this way, a rope is needed. One of these ropes is part of the emergency equipment of both, the PIC and the PNF/FO and is found in a storage located on the upper side to of the cockpit to the left and right.
Smaller aircraft and general aviation planes usually don't employ a separate cockpit. Cabin and cockpit are just one big space.
Cheers

If necessary, the cockpit ropes can be used to evacuate people other than just the pilots; I can't recall off the top of my head which one precisely it was, but I've read about a runway overrun by a DC-10 where all the slides were popped by fire before everyone was able to evacuate, and the last few passengers and cabin crew had to slide down the cockpit ropes.

Update: I was thinking of Continental 603.

I have not known! Thanks for sharing.

Note that older aircraft did have separate cockpit door, e.g. Lockheed Constellation. But they still had the door from cockpit to cabin, because why not.


text:
What qualifies as a "takeoff" and "landing" in currency requirements?
I just met my night-time currency requirements at KONT.
Landing and taking off from a 12000 foot runway in a Cessna 152 got me to thinking (always dangerous, I know).
There's more than enough room to land to a full stop, take off, climb to (e.g. 50 feet AGL), then immediately land again to a full stop without needing to go around the pattern.
Could doing the above count as two takeoffs and landings?
Perusing FAR 61.57 did not give me an answer.
Now I'm not suggesting that this is a good idea, but brings up a few questions;
1)  Is this a legal maneuver?
2) If so, would it meet currency requirements? (If not, chapter/verse of the regulations kindly requested).
3)  Assuming it's ok with the tower, how would I request such a move?

If I could find a citation, I would have included it as an answer - this came up at a FAA seminar were certain maintenance actions require a check flight. The FAA views a landing as going from normal cruise to the landing configuration with full stop. So, if you can get the flaps up, throttle and speed set to cruise and still land full stop - it would count. The only reason I can think that the FAA might disqualify this is most 12,000ft runways have glide slope indicators such as VASI and you are required to use it when available. I.E a large dry lake bed would allow multiple straight in.

It's shortcuts like this that usually result in accidents. Why wouldn't you want to practice your climb-out and approach too?

There's more than enough room to land to a full stop, take off, climb to (e.g. 50 feet AGL), then immediately land again to a full stop without needing to go around the pattern.

50 feet is completely arbitrary. Why not 5 feet? If the wheels leave the ground and touch back down, you took off and landed didn't you?
The regs exist to make sure you're maintaining some basic proficiency. Cutting corners to fulfill the letter of the law without actually refreshing your skills does no one any good — least of all you. Besides, as jwzumwalt pointed out, it most likely wouldn't meet the FAA's definition of takeoff and landing.

You are asking three different questions; I will answer the second.
CFR 61.57 specifies three takeoffs and landings are required in 90 days to satisfy general and night experience requirements. For instrument experience, the same section requires six IFR approaches, holding procedures, etc.
Since approaches are specifically required for instrument experience, the lack of specific requirement for night and general experience means your proposal should fit within the regs for currency. I could find no Advisory Circular to the contrary.
It does not mean that it is smart or legal at that airport.


text:
Is a cambered or symmetrical propeller airfoil more efficient?
Is an cambered propeller more efficient than a symmetrical propeller for a low speed airplane?

Your pictured symmetrical airfoil is actually cambered.

Yeah!....but hey it looks identical to a symmetrical airfoil

Cambered airfoils are used on propellers as they create less drag for a given Cl than a similar symmetrical airfoil.
The primary use for uncambered or symmetrical airfoils is on flight surfaces that must provide lift in both directions equally well, as in a vertical tail or aerobatic aircraft wing. Propellers only provide forward lift or thrust (ground reverse is too little used to matter) so camber works better.

You might mention that camber will cause the blade to twist, reducing the benefit of camber. Therefore, propeller airfoils only have light camber.


text:
Why doesn't G-force knock this pilot out twice?
In this video an F-16 goes into a dive after the pilot loses consciousness. The Auto-GCAS corrects to avoid a crash, and the pilot regains consciousness and pulls up even harder. Why doesn't he pass out a second time?
According to this article and the G-force meter (at the top left) the pilot:

Goes into turn and loses consciousness at about 8g's.
The Auto-GCAS rolls and pulls up to a limit of 5g's.
The pilot recovers consciousness and pulls up to 9.1g's.
Pilot responds to radio calls to cancel the exercise and gain altitude.

It seems he held the recovery for quite a bit longer and at higher G-forces than the turn that made him pass out. I assume he also didn't have time to do anything breathing exercises or preparations for a high g maneuver. He is also experiencing the G-forces in the same direction both times (pulling back on the stick).
So why didn't the pilot pass out the second time?

Because pilots are not machines. "I assume" is what makes this question a little shakey.

Your body responds to a lack of oxygen to the brain with physiological responses that can take up to ten seconds to be effective.

...The brain is highly sensitive to cellular hypoxia (lack of oxygen), so rapid impaired function and almost unconsciousness follows (A-LOC), and then ultimately total unconsciousness (G-LOC). To avoid this, your body will reflexively make adjustments in heart output and blood pressure to increase blood flow to the brain (by parasympathetic response–an adrenaline surge), but it takes 6-9 seconds for this reflex to initiate.  By this time, unconsciousness has likely occurred, which obviously means no one is conscious to fly the aircraft.

Raptor 9.0g turn

In addition, the pilot likely made greater effort to avoid a second blackout.

Breathing: Rapid (< 1 sec) exhalation/inspiration cycles every 3 seconds.  This maintains oxygen content and decreases carbon dioxide in blood, while also relieving increased pressure of chest, and allowing the heart to refill with deoxygenated blood from the rest of the body.

Isometric Contraction:  Flexion of skeletal muscles of legs and abdomen.  When muscles contract, the small blood vessels in them constrict, making them smaller with less room for blood.  This step increases pressure in chest and displaces blood away from these contracted muscles into the upper body and brain.

Together, some combination of these measures would prevent a repeat blackout.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/